Mode-division multiplexing (MDM) technology enables high-bandwidth data transmission using orthogonal waveguide modes to construct parallel data streams. However, few demonstrations have been realized for generating and supporting high-order modes, mainly due to the intrinsic large material group-velocity dispersion (GVD), which make it challenging to selectively couple different-order spatial modes. We show the feasibility of on-chip GVD engineering by introducing a gradient-index metamaterial structure, which enables a robust and fully scalable MDM process. We demonstrate a record-high-order MDM device that supports TE₀–TE₁₅ modes simultaneously. 40-GBaud 16-ary quadrature amplitude modulation signals encoded on 16 mode channels contribute to a 2.162 Tbit / s net data rate, which is the highest data rate ever reported for an on-chip single-wavelength transmission. Our method can effectively expand the number of channels provided by MDM technology and promote the emerging research fields with great demand for parallelism, such as high-capacity optical interconnects, high-dimensional quantum communications, and large-scale neural networks.

We propose to use the low-coherence property of amplified spontaneous emission (ASE) noise to mitigate optical crosstalk, such as spatial, polarization, and modal crosstalk, which currently limits the density of photonic integration and fibers for dense space-division multiplexing. High optical crosstalk tolerance can be achieved by ASE-based low-coherence matched detection, which avoids dedicated optical lasers and uses spectrally filtered ASE noise as the signal carrier and as a matched local oscillator. We experimentally demonstrate spatial and modal crosstalk reduction in multimode fiber (MMF) and realize mode- and wavelength-multiplexed transmission over 1.5-km MMF supporting three spatial modes using a single ASE source. Performance degradation due to model dispersion over MMF is experimentally investigated.